User login

Venetian Influence and the Invention of Lead Crystal

Part 2. Venetian Influence and the Discovery of Lead Crystal. (1674 - 1700)

Set of Venetian nesting beakers: If the glasses ordered from Venice between 1677 and 1673 by London merchant, John Greene. They were discovered in a rubbish pit in Tunsgate, Guildford.

If the glasses ordered from Venice between 1677 and 1673 by Pondon dealer, John Greene are anything to go by, English taste was both simple and conservative. The remains of a nesting set of beer glasses excavated from a rubbish pit in Tunsgate, Guildford is a unique example.

But the Venetian glassblowers were capable of much better things than this as illustrated by extraordinary confections in the Fitzwilliam collections. The 16th century two-handled vase, or cup, exploits every trick in the glassblower's locker, a creation that would challenge the skill of most glassmakers today. The bowl is blown glass but the foot is shaped from clear and opaque white rods fused side Venetian vase, late 16th century. Ht. 15.3cm (C131.1912)byVenetian bobbin stem goblet and cover. Ht. 37.1cm (C132.1912) side, rolled to form a tube closed at one end and then blown. White threads are twisted into clear glass canes (latticinio) to make the handles and applied trimmings while more white threads form an X-pattern round the base of the bowl in the manner of gadrooning.

In the other piece illustrated here canes with different patterns are fused side-by-side and formed into a tube before blowing into a tall goblet and cover. It is not surprising that the Venetians held world dominance in glass making. How could England expect to compete with such closely guarded talent? But form and decoration were not the only requirements in demand, particularly for more general use. The quality of the glass was still relatively poor and the great challenge was to match the clarity of rock crystal. John Evelyn's account of his Grand Tour (1643 - 1651) makes numerous references to the impressive collections of rock crystal he saw on his travels.

George Ravenscroft had spent some time as a merchant in Venice from where he brought luxury goods, such as lace, to England. Back in the home country he met up with an Italian glassmaker, John Baptista da Costa. Da Costa was not an ordinary glassmaker but specialised in bijouterie, for which I believe Ravenscroft saw a commercial opening to his rich clientelle.

Posset pot with gadrooned base and Ravenscroft seal on spout (shown above). 1677-1678. Ht. 7cm. (C964.1961)Ravenscroft built da Costa a furnace in the semi-derelict Savoy palace where the Italian set to work making a rare and expensive form of multicoloured glass known as calcedonio. This glass is unusual that in order to make it a pure cristal, containing lead, is first prepared and the complex colouring mixture then stirred into it.

Ravenscroft must have seen this preliminary cristal and recognised its superiority, not just for tableware but also for making mirrors, the most profitable manufacture for glass at that time. An additional benefit that made the lead crystal a marketable proposition was that it was English practice to add saltpetre to the batch to counter the deleterious effect of the coal-fired furnace (see part 1).

The oxidation propertied of the saltpetre fortuitously solved another problem caused by molten free lead in the glass, namely that the lead would otherwise attack and destroy the pots as recorded in detail by Neri in his book The Art of Glass. The saltpetre prevents this by keeping it as lead oxide (or, more properly, Pb 3+ ions).

Thus English lead crystal was born out of a series of chance events. But problems still remained; without the Posset pot sealed with the letter S on the base of the spout, c. 1680. Ht. 8.5 cm. added colouring powder and even with the addition of lead (about 15%) the glass crizzled. It took another year or so of research to solve this problem, marked by the addition of a seal to identify the new high-lead glass further confirmed by the way it rang when struck.

The new English metal proved superior to Venice cristal and although attempts were made on the Continent to copy Ravenscroft's discovery it dominated the market for the next century.

The temporal sequence of events was as follows:-

1673, May 29th. Ravenscroft sets up glass furnace for da Costa in the Savoy (near where the Savoy Hotel now stands in London's Strand).

1674, March 19th. Patent granted for 7 years to make "cristall for drinking glasses".

1674, April. Agreement with Glass Sellers to take all his output plus permission to set up a second glasshouse at Henley on Thames.

1675. Not documented but the new crystal found to crizzle (crystalise and fall to pieces) due to an imbalance of the ingredients.

1676, June 3rd. "Crizzling redressed several months ago", the glasses identified by the "distinction of sound discernable by any person whatsoever".

1682, February. The Glass Sellers, having taken a lease of the Savoy glasshouse, late in occupation of G. Ravenscroft, employ Hawley Bishopp to make "christalline or flint glass" there.

1688, April. H. Bishopp still at work in the Savoy.

It is this act of sealing the glasses that enables us to identify some forty remaining Ravenscroft glasses today. Some have crizzled in the ensuing 300 years, part of this being due to poor storage. The Venetian ambassador was horrified when he first saw the new lead crystal, and rightly so, much of the substantial Venetian market was soon destroyed as the London glassmakers turned enthusiastically to the new metal.

Dish and stand with Ravenscroft seal. c.1676-1677. Diam. of bowl 17.8cm; Diam. of stand 24.1cm. (612a-b.1961)The Fitzwilliam also has a sealed Ravenscroft bowl and stand (shown right) and a number of unsealed ones attributed to his glasshouse. Several of the glasses in the collection were probably made either by his brother, Francis or by Hawley Bishopp, both of whom took over the Savoy glasshouse after Ravenscroft. Illustrated is a badly crizzled posset pot sealed with the letter "S", possibly standing for "Savoy.

As other glassmakers learned how to make lead crystal, adding a seal to indicate authenticity, or perhaps ownership, became popular. Consequently, there are a number of glasses of this period with different seals or with indecipherable seals. The important thing to remember is that the role of the seal was to establish identity as well as give quality assurance and it should therefore be clear and easily recognised.